From TekWiki
Jump to navigation Jump to search
Tektronix 549
30 MHz storage scope
Tektronix 549 front

Produced from 1965 to 1974

Manuals – Specifications – Links – Pictures

The Tektronix 549 is the only storage scope in the 500 series (except for the 537 that never left prototype stage).

It takes a letter-series or 1-series vertical plug-in. The 549 was introduced in 1966 and discontinued after 1973.

The 549 vertical output stage was designed by Mel Holtznagel. Bob Shand did the mechanical design.

Key Specifications

Bandwidth DC to 30 MHz (−3 dB) with fast plug-ins (1A1, 1A2, 1A4, 1A5)
Rise time 12 ns
Writing speed 5 cm/μs
Line voltage 104/115/127 or 208/230/254 VAC ±10%, selected via primary voltage selector (inside cabinet) and voltage range selector (on rear panel), 50 to 60 Hz
Thermal protection 65°C (150°F) Automatic resetting thermal cutoff
Power consumption 650 W, 750 VA
Size 43.2 cm × 32.9 cm × 60.7 cm (W/L/H, 13" × 24" × 17")
Weight 31 kg (68 lb)
Cooling AC Fan
Construction Aluminum alloy chassis, anodized front panel, blue vinyl coated cabinet


Mix of Transistors and Tubes

Like many Tek scopes from the period, the 549 uses a mix of transistors and tubes. For example, consider the buffer amplifier in the 549, whose purpose is to interface the high-impedance output of the plug-in with the low-impedance of the 200 ns delay line in the 549. As is usual in oscilloscope vertical circuits, the requirement is to have flat frequency response from DC to the maximum frequency of the scope and to have linear phase response over this same frequency range.

In the 549, this buffer is implemented with a 6DJ8 cathode follower at the plug-in interface driving an NPN BJT differential amplifier at the bottom of a cascode with a 7119 tube on top. The output of the cascode (the plate of the 7119) drives the delay line.

Since the entire signal path is differential, the common-mode voltage does not have to be zero, and it is not; the differential signal in the delay line rides on 167 volts of DC.

After the delay line, the signal enters another cascoded differential amplifier with NPN BJTs on the bottom and a pair of 10-watt 8608 power pentodes on the top whose plates drive the CRT's vertical deflection plates of the CRT through inductive matching/peaking networks.

Non-Distributed Amplifier

The 549 is slightly unusual among 54x-series scopes in that it does not use a distributed vertical amplifier. (Other exceptions include the 545B and 547).


Triggering is done using an NPN BJT Schmitt trigger.


The 549 uses the T5490 CRT which has two storage targets, upper and lower, whose storage mode and erase signals can be controlled independently. There is a remote control cable/switch, part number 012-0102-00 (photo below), that can erase the screen and reset the single sweep. It connects to an Amphenol 165-16 socket at the rear top of the scope (see 549 remote control connector for pin-out).

Power Supply

The 549's power supply provides regulated outputs of −12.4 V, −150 V, +100 V, +225 V, +300 V, +350 V, and +500 V as well as a +475 V unregulated output.

Line input is connected to main transformer primary via two switches, one inside the chassis to select the 110 V or 230 V range, and another on the rear of the chassis to select Low/Medium/High voltage in either range.

Multiple secondary windings feeds diodes for rectification for different voltages. Both center-tap and bridge configuration is used. Transistors and/or tubes are used for regulation.

As is common in many Tektronix scopes, all regulated voltages are referred to the negative regulated rail (−150 V in this case) by fixed low-tolerance dividers. Only the −150 V voltage is trimmed, its reference is a 5651 VR tube. A 12AX7 is used as the comparator, three 12B4 in parallel are used as series pass tubes. A 6AU6 is used as an error amplifier.

Most other stages replicate the same design, except slight changes in tubes used − the +350 V, +225 V and +100 V regulators employ a 6080 as the pass element.

The −12.4 V regulator is transistor-based.

The 549 power supply uses a 6N030 delay relay (P/N 148-0021-00) to control a relay that switches supply voltages on only after the tubes are warmed up. On power up, only heater voltage is applied to the tubes. After a delay of up to 60 seconds, the thermal delay relay activates the main relay (driven from unregulated +170 V). This also cuts out the delay relay, which can cool down and will be ready to delay again even after a quick interrupt in power input.

The 549 has a 65°C (150°F) thermal cutoff.

The 549 uses a 120-0423-00 HV transformer driven by a 6GF5 tube from +470 V.

HV Transformer Problem and Replacement

The HV transformer (part #120-0423-00) uses epoxy impregnation like models 544,545B,546,547,556 and as such suffers the same issue of increasing losses with age unlike the earlier bee's wax transformers. This issue will eventually lead to failure of the HV oscillator circuit resulting in loss of display intensity, blooming and finally vanishing trace. One solution is to use a donor HV transformer out of a 564 storage scope. This was successfully implemented by Morris Odell and Deon Vandenberg however invented by another. A photo is provided below showing the new transformer installed with terminals arbitrarily labelled to help others perform the same task. Looking at the photo the top connections are obvious. The left middle connection goes to the right strip pin 9 (labelled as 9) The bottom section has two connections, one on the left towards the neons(labelled A) this goes to the anode of the driver tube V800 pin 7. The other obscured wire is the bottom left which goes to the 4th pin on the left strip (labelled as 4). Resistor R807 is to be changed from 39k to 47k. Resistor R2 is to be added between the junction of D836 and C842 and R837. (See schematic.) When this is done adjust the HT at the test point to -3700V (R855) and adjust R815 to make the grid voltage -3790V (located at test point labelled TP). To see the new transformer in action click on the bottom youtube link.



Remote Control


HT Transformer modification

Some Parts Used in the 549

Page Class Description Used in
12AL5 Vacuum Tube (Double Diode) high-perveance dual diode 545 545A 549 N
12AU6 Vacuum Tube (Pentode) RF pentode 81 112 512 556 575 545 549 581 585 A B C G K H L M N O R S Z
12AU7 Vacuum Tube (Dual Triode) dual medium-μ triode 122 160 161 162 181 190 310 316 317 502 502A 512 516 517 517A 526 535 536 545 545A 545B 547 549 555 575 581 581A 585 585A C D E N Q
12AX7 Vacuum Tube (Dual Triode) dual triode 513 531 531A 535 536 545 545A 545B 546 547 549 555 581 581A 585 585A E Q
12B4 Vacuum Tube (Triode) power triode 126 310 310A 316 317 502 502A 526 541 541A 535 535A 545 545A 546 547 549 551 555 513 581 581A 585 585A
12BY7 Vacuum Tube (Pentode) miniature 6.5 W power pentode 106 163 531 533 535 536 541 543 535 545 545A 549 555 3A75
6080 Vacuum Tube (Dual Triode) dual power triode 132 160 316 317 535 535A RM35A 541 541A 535 536 545 545A 545B 546 547 549 575 581 581A 585 585A
6AL5 Vacuum Tube (Dual Diode) high-perveance dual diode 163 181 190 310 310A 315 316 317 502 502A 503 511 511A 512 516 517 517A 526 535 535A 545 545A 549 581 581A 585 585A 551 C T Telequipment S52
6AU6 Vacuum Tube (Pentode) RF pentode 2A60 80 107 160 181 190 310 310A 316 317 360 502 502A 512 513 516 517 517A 526 529 RM529 531 531A 535 536 545 545A 546 547 549 555 575 581 581A 585 585A C CA Q
6BL8 Vacuum Tube (Triode/Pentode) triode-pentode combo 503 504 516 549 Telequipment D52 Telequipment S31 Telequipment S32 Telequipment S32A Telequipment S51 Telequipment S52
6CL6 Vacuum Tube (Pentode) miniature power pentode 132 310 310A 316 317 515 524 525 531 535 535A 545 545A 545B 549 581 581A 585 585A 3A74
6DJ8 Vacuum Tube (Dual Triode) dual triode 80 132 161 310A 316 317 3A75 502 502A 503 504 515 516 519 526 529 RM529 533 535 536 543 544 545 545A 545B 546 547 549 555 556 565 581 581A 585 585A 661 2A60 63 2A63 3A7 3A8 1121 1A4 67 81 82 86 3B1 3B4 1S1 B O W Z Telequipment S32A Telequipment D52 Telequipment TD51 Telequipment S52 Telequipment S51 Telequipment Type A
6GF5 Vacuum Tube (Pentode) high voltage 9 Watt beam-power pentode 549 556
7119 Vacuum Tube (Dual Triode) dual triode 067-0532-00 191 3A3 3B4 3B5 516 545B 549 661
8426 Vacuum Tube (Pentode) RF pentode O 545A 549 581A 585A
8608 Vacuum Tube (Pentode) 10-watt power pentode 549 556 3A7
T5490 CRT direct-view storage CRT 549